The London phone book, 1939.  Pretty neat find at the NYPL!

I would say that is certainly an illustration of a bed bug on that advertisement on the edge, not a beetle.

1. Compare with a modern illustration.
2. Consider that there were 4 million Londoners estimated to have bed bugs in 1939 (Dr. Snetsinger in Mallis (1997), citing R.I. Sailer).
3. The population of greater London at the 1939 census was 8,615,050.
4. Therefore, some 46% of the city had bed bugs. Which would be lower than the high 50% estimate of a few years prior:

As a result of a questionnaire addressed to the London County Council, the Councils of the City of London and of the Metropolitan and County Boroughs, it has been possible to form some opinion as to the extent of the problem. Estimates of the amount of infestation of houses provided under the various Housing Acts since that of 1919 vary greatly, some estimates being in the neighbourhood of 50 per cent.

Virtually every urban authority is more-or less troubled with this problem. It is estimated that in many areas practically all the houses are to a greater or less degree infested with Bed-bugs.

Ministry of Health Report No. 72, Report on the Bed-Bug (1933) Report of the Committee on the Eradication of Bed-Bugs. HMSO. (We highlighted some other great quotes from this report previously here.)

We should also note that in Britain in 1939, bug could only mean bed bug, old Cimex l. See Mr. Mencken.

So, definitely a bed bug, from a time and a place when there were bed bugs everywhere. Something to think about, as always.  Awesome, Nobugs.  But what was the name of the firm?